Philippines: Island of Mindoro

Called the dark island by outsiders because of a virulent strain of malaria, Mindoro is located between the large islands of Luzon and the Sunda-affiliated Palawan, and it shares faunal attributes of both islands. However, Mindoro was isolated from Luzon and Palawan throughout the Pleistocene and retains its own unique character, including an endemic water buffalo species (Heaney 1986). Unfortunately, Mindoro is one of the most severely deforested islands in the country (Heaney and Mittermeir 1997). Only the most rugged portions of the island's central spine has been spared from commercial logging, and the forest is still under pressure.

Scientific Code

(IM0130)

Ecoregion Category

Indo-Malayan

Size

3,900 square miles

Status

Critical/Endangered

Habitats

Description Location and General DescriptionThis ecoregion includes the island of Mindoro and the Semirara Islands. The climate of the ecoregion is tropical wet (National Geographic Society 1999). The western coast of Mindoro experiences a wet season during the southwest monsoon of June to October and a dry season during the November to February northeast monsoon because of the central mountains (High Rolling Mountains) (Collins et al. 1991). The High Rolling Mountains dominate the central portions of the island and rise to a maximum elevation of approximately 2,500 m at Mt. Halcon and Mt. Baco.

Mindoro (along with Palawan and the Calamianes) was rifted (below water) from the Asian mainland approximately 32 million years ago, transported through seafloor spreading across the growing South China Sea, added to the growing Philippine Archipelago approximately 17 million years ago, and uplifted above water approximately 5-10 million years ago (Hall and Holloway 1998; Dickinson, Kennedy, and Parkes 1991). Mindoro is separated from Palawan to the south and Luzon to the north by deepwater channels and has not been connected to those islands during the recent past (Pleistocene) (Heaney 1986).

Vegetation types on Mindoro include lowland evergreen rain forest to approximately 400 m or higher, open forest from about 650 to 1,000 m, and mossy forest above. Only small patches remain of the lowland evergreen dipterocarp rain forest that would have dominated the lowland eastern portions of the island. Semideciduous forest would have predominated on the western half of the island. Limited stands of Mindoro pine (Pinus merkusii) are found at elevations of 600 m or less in the northern portions of the island (Stattersfield et al. 1998; Development Alternatives 1992).

Biodiversity FeaturesOf the forty-two indigenous mammal species found on Mindoro, close to 20 percent endemic or near endemic (table 1). The nonendemic mammals are also found on Luzon. An endemic rat (Rattus mindorenis) is closely related to Rattus tiomanicus, and the endemic genus Anonomomys is most closely related to the genus Haeromys, from Palawan and some of its satellite islands. Thus colonization of Mindoro has occurred from both Luzon and Palawan (Heaney 1986).

An asterisk signifies that the species' range is limited to this ecoregion.

The most unique animal feature of Mindoro must be the tamaraw (Bubalus mindorensis), or dwarf water buffalo. There were perhaps 10,000 living at all elevations on the island at the turn of the century. The tamaraw, like the anoas of Sulawesi (Anoa spp.), are wary forest animals, just over 1 m tall at the shoulder (Heaney and Regalado 1998; Nowak 1999a). Tamaraws sometimes are placed in the same genus as anoas. They should not be confused with the carabao of the Philippines, which is a small variety of domesticated Asian water buffalo (B. bubalus). The tamaraw needs both dense vegetation for resting and open grazing land. It is unclear whether tamaraws need wallows. Unfortunately, they are confined to areas of grassland that have taken the place of the native forest. Adult bulls are largely solitary and aggressive toward each other. Young males (up to five years) form bachelor groups. Females are found alone, with a bull, or with up to three young of differing ages. Young are born during Mindoro's June-November rainy season and stay with their mother until the age of 1.5 to 4.5 years (Nowak 1999a).

Mindoro also supports a population of the Philippine warty pig (Sus philippensis), which the IUCN considers rare and declining (IUCN 2000). The Philippine warty pig is widely distributed in the still-forested areas of Luzon, Mindoro, Samar, Leyte, Mindanao, and some of the smaller satellite islands. Many of these forested areas are found in existing national parks. The Philippine warty pig is closely related to Sus barbatus of the Greater Sundas and was once thought to be a subspecies, analogous to the Palawan bearded pig (Sus barbatus ahoenobarbus). This species is still threatened by hunting and habitat loss (Oliver 1993).

An endemic subspecies of the Philippine deer (Cervus mariannus barandanus) is found on Mindoro. Although Philippine deer are native to Luzon, Mindoro, Samar, Leyte, Mindanao, and the Basilan Islands, C. m. barandanus is found only on Mindoro. The population of this subspecies is considered to be at risk over its limited range on the island (Wemmer 1998).

This ecoregion corresponds exactly with the Mindoro EBA. The Mindoro EBA contains ten restricted-range birds, six of which are threatened. The Mindoro ecoregion contains eleven endemic or near-endemic bird species (Kennedy et al. 2000; table 2). Two bird species, the Mindoro bleeding-heart (Gallicolumba platenae) and the black-hooded coucal (Centropus steerii), are considered critically endangered, and four species are considered vulnerable: Mindoro imperial-pigeon (Ducula mindorensis), ashy thrush (Zoothera cinerea), Luzon water-redstart (Rhyacornis albiventris), and scarlet-collared flowerpecker (Dicaeum retrocinctum). Three of these species, the Mindoro bleeding-heart, the Mindoro imperial pigeon, and the black-hooded coucal, are strict island endemics (Collar et al. 1999; Stattersfield et al. 1998). Mindoro's endemic birds can be split into montane and lowland species. Although both are in urgent need of conservation, the situation for the lowland species is particularly dire because the lowland forests are almost entirely gone (Dutson et al. 1992). Mindoro is also an important wintering and staging area for ducks and other waterbirds (Bagarinao 1998).

An asterisk signifies that the species' range is limited to this ecoregion.

The type specimen of the critically endangered Philippine crocodile (Crocodylus mindorensis) was collected in Mindoro's Naujan Lake (Bagarinao 1998). They were historically found on the islands of Luzon, Mindoro, Masbate, Samar, Jolo, Negros, Busuanga, and Mindanao, but the only remaining populations are found on Mindoro, Negros, Mindanao, and Busuanga. The only protected population of Philippine crocodiles is in Lake Naujan National Park on Mindoro. Whereas the decline of the species initially was driven by overexploitation, habitat loss and human persecution are now the principal threats to the Philippine crocodile. Surveys in 1980-1982 revealed a total wild population of approximately 500-1,000 individuals, but current wild populations may be approximately 100 nonhatchlings. Captive breeding efforts are being led by the Crocodile Farming Institute, an entity of the Philippine government (Ross 1998; IUCN 2000).

Lubang Island, near Mindoro and Luzon, is a poorly known island surrounded by deep water channels; it may well represent a small but distinct center of endemism (L. Heaney, pers. comm., 2000).

Current StatusThe only remaining intact forests in Mindoro are found along the top of the mountain ridge that divides the island. On the eastern side of the ridge commercial logging ended long enough ago that the remaining intact forests are buffered by secondary forests that have reestablished a closed condition, yet these same forests are again under threat from poaching and kaingin (slash-and-burn) agriculture. On the western side of the ridges, however, perennial fires in adjacent grasslands used for pasture are eating into the forest (Development Alternatives 1992). Only 8.5 percent of Mindoro was forested in 1988 (SSC 1988).

Several reserves have been established in Mindoro, beginning in 1936, but these have proved to be less than effective (Heaney and Regalado 1998). Table 3 details the existing protected areas on the island.

Ecoregion numbers of protected areas that overlap with additional ecoregions are listed in brackets.

The largest protected area on Mindoro is Mounts Iglit-Baco National Park, which is one of two ASEAN Natural Heritage Sites in the Philippines (the other is Mount Apo National Park on Mindanao). The park covers the east-west divide and includes several physiographic regions and an important tamaraw population. Small patches of dipterocarp and mossy forest can be found in the park. The park is inhabited by the Mangyan tribal people, and much of the reserve consists of fire-maintained grassland with Imperata cylindrica and Sacchareum spontaneum. The combination of burning to maintain pasture for domestic cattle, ranching, and uncontrolled hunting activities leaves this protected area substantially altered, and the park is an insecure refuge for the endangered tamaraw (Collins et al. 1991).

Lake Naujan National Park is the only protected area in the Philippines that protects the critically endangered Philippine crocodile (Ross 1998).

The tamaraw numbered approximately 10,000 animals at the turn of the century and approximately 1,000 by 1949, and today estimates range from 100 to 200 animals (Collins et al. 1991; Heaney and Regalado 1998).

A well-funded conservation program aimed at captive breeding of tamaraws has been an expensive failure (Heaney and Regalado 1998).

Types and Severity of ThreatsHunting by local people is a threat to all large mammals in the ecoregion, including the tamaraw, Philippine deer, and Philippine warty pig (Hedges, in press). Forestry activities and kaingin (slash-and-burn) agriculture continue to fragment and destroy the remaining habitat.

Although it is smaller and not as rich as some of the larger Philippine islands, Mindoro faces high levels of faunal endangerment because a larger proportion of its fauna is endangered; this level of endangerment is well-correlated with the degree of deforestation on the respective islands (Heaney 1993).

Justification of Ecoregion DelineationMacKinnon (1997) identified seven subunits in the Philippines, and the Philippine Biodiversity Action Plan (Philippine BAP 1997) demarcated fifteen biogeographic units. Udvardy (1975) identified the Philippines as a single biogeographic province. We delineated nine ecoregions in the Philippine islands, including Palawan. We deviated from Udvardy (1975), MacKinnon (1997), Stattersfield (1998), and the Philippine BAP (1997) in varying degrees and based our delineation of the Philippine ecoregions on Heaney (1993). MacKinnon (1997) designates Mindoro island as subunit 26f and includes the Lubang Islands. We delineated the island of Mindoro as the Mindoro Rain Forests [IM0130].

ReferencesReferences for this ecoregion are currently consolidated in one document for the entire Indo-Pacific realm.Indo-Pacific Reference List